In general a catheter is a device for transporting a fluid to or from a body cavity. Often catheters comprise a tube-shaped part which facilitates the fluid transport.
A subgroup of catheters is known as soft needle catheters and they have a wide range of applications, e.g. in automated drug delivery devices such as insulin delivery devices. The soft needle catheters are in general more flexible and softer than other catheters.
The soft needle catheters are generally used together with an Introducer needle, where the needle is used to penetrate the barrier to the body e.g. the skin and assist the introduction of the catheter. The needle is removed after introduction of the catheter into a body cavity. The soft needle catheter is left in the body cavity for a desired period of time in which it functions as the means for drug delivery. The soft needle catheter is removed from the body cavity, by simple withdrawing after end of use.
A soft needle catheter often comprises a tube-shaped flexible part and a hub. The tube-shaped flexible part is adapted for insertion into a patient and it facilitates the fluid transport to or from a body cavity. The tube-shaped part must be flexible in order to allow the carrier of the catheter, e.g. a patient, to move without serious unpleasantness. However it must not be so flexible that it is capable of forming kinks which may stop the drug delivery. The hub is the connecting means on the tube shaped part adapted for connecting the tube shaped part to either the drug delivery devise, to the fluid collecting container or to another connecting means e.g. a second tube.
Soft needle catheters can be manufactured as one-piece catheters or two-piece catheters, where the tube-shaped part and the hub are made separately. A two piece catheter is easier to manufacture but it suffers from the drawback that there is a risk of separation, especially during removal of the catheter, leaving the tube-shaped part in the body cavity. Therefore one-piece soft needle catheters are preferred.
Moulding of one-piece soft needle catheters is complicated due to the dimensions of the catheter. There is a risk that the tube-shaped part wrinkles during removal from the mould form either as a consequence of the withdrawal of the core creating the hollow part or as a consequence of sticking to the mould.
Different approaches to the manufacture of one-piece soft catheters are known from the literature.
EP 1 116 567 A2 discloses a method using gas assisted injection moulding and a mould which splits perpendicular to the axis of the tube-shaped part, approximately on the middle. During moulding there is a risk that a fin forms at the splitting line of the mould. A fin placed at the middle of the tube-shaped part might cause unnecessary pain or even cuts to a patient during penetrations of the skin.
GB 819 225 discloses a method for injection moulding of a silicone rubber self-retaining catheter adapted to receive a stopper, where a wire is used as the moulding core.
WO 90/00960 discloses a method of producing soft needle catheters in which a sleeve is mounted on the core of the mould. The sleeve assists the removal of the core after curing. Use of sleeves complicates the production and increases the production costs.
Therefore it is desirable to have a new method for production of soft needle catheters which can avoid the drawbacks of the prior art.